1. Field of the Invention
Embodiments of the present invention relate to an apparatus and a method for measuring a thickness of a substrate. This application relies for priority upon Korean Patent Application No. 2003-55084 filed on Aug. 08, 2003, the content of which are herein incorporated by reference in its entirety.
2. Description of the Related Art
Monocrystalline silicon, which is a raw material for a semiconductor device, is formed into a cylindrical ingot through a Czochralski crystal growth method. The ingot of monocrystalline silicon is manufactured into silicon wafers through a series of wafer processes including a slicing process, an etching process, a cleaning process, and a polishing process. The silicon wafer can be used as a semiconductor substrate. A semiconductor device can be fabricated through a series of unit processes performed on the semiconductor substrate including a deposition process, a photolithography process, an etching process, an ion implanting process, or a chemical mechanical polishing process.
Various sizes of the silicon wafer (e.g. 6 inch, 8 inch, and 12 inch) may be utilized in fabricating semiconductor devices. As semiconductor technology evolves, the thickness of silicon wafers has been decreasing. For example, a 8 inch wafer has a thickness of about 755 μm, and a 12 inch wafer has a thickness of about 775 μm.
Measurement of wafer thickness can be important in the inspection process of a semiconductor device. Accuracy of measurements of wafer thickness should have an allowable error ±0.5 μm. A capacitive sensor may be used for measuring the wafer thickness. U.S. Pat. No. 6,353,473 (issued to Ishimori et. al.) discloses a measurement apparatus for measuring the wafer thickness including an optical heterodyne interferometer. However, the capacitive sensor can be limiting, because the wafer thickness can not be measured with constant density. Also, the measurement apparatus disclosed in U.S. Pat. No. 6,353,473 may be disadvantageous because both the measurement method and the structure of the apparatus are relatively complicated.